Microstructure, Mechanical Properties, and Corrosion Resistance of Ag–Cu Alloys with La2O3 Fabricated by Selective Laser Melting

Abstract

Ag and its alloys, when prepared by a selective laser melting (SLM) process, have a low density and poor overall performance due to their high reflectivity when the most commonly used laser (λ = 1060 nm) is used, and they have exorbitant thermal conductivity. These characteristics lead to the insufficient melting of the powders and severely limit the applications of additive manufactured silver alloys. To improve the absorption of the laser, as well as for better mechanical properties and higher resistance to sulfidation, Ag–Cu alloys with different La2O3 contents were prepared in this work using the SLM process, via the mechanical mixing of La2O3 nanoparticles with Ag–Cu alloy powders. A series of analyses and tests were conducted to study the effects of La2O3 in Ag–Cu alloys on their density, microstructure, mechanical properties, and corrosion resistance. The results revealed that the addition of La2O3 particles to Ag–Cu alloy powders improved the laser absorptivity and reduced defects during the SLM process, leading to a significant rise from 7.76 g/cm3 to 9.16 g/cm3 in the density of the Ag–Cu alloys. The phase composition of the Ag–Cu alloys prepared by SLM was Silver-3C. La2O3 addition had no influence on the phase composition, but refined the grains of the Ag–Cu alloys by inhibiting the growth of columnar grains during the SLM process. No remarkable preferred orientation existed in all the samples prepared with or without La2O3. An upwards trend was achieved in the hardness of the Ag–Cu alloy by increasing the contents of La2O3 from 0 to 1.2%, and the average hardness was enhanced significantly, from 0.97 GPa to 2.88 GPa when the alloy contained 1.2% La2O3 due to the reduced pore defects and the refined grains resulting from the effects of the La2O3. EIS and PD tests of the samples in 1% Na2S solution proved that La2O3 addition improved the corrosion resistance of the Ag–Cu alloys practically and efficaciously. The samples containing La2O3 exhibited higher impedance values and lower corrosion current densities.

Silver Alloy Surface Modification for Mechanical Property Enhancement in Aviation and Transportation

“…It is difficult to find publications in the scientific literature discussing the impact of Cr and Ni additions on the structure and properties of laser-melted silver. Publications most often discuss the impact of laser melting on the structure and properties of pure silver and 925 silver [1,30,31] and investigations concerning silver alloys with the addition of Cu, C, and W [32], or the alloy Ag-Cu [2,33]. Investigations concerning the alloy Ag-Cu-Ge have also been published [34].…”

“…It was found that the processing of Ag-Cu alloys using SLM (selective laser melting) inhibits the growth of columnar grains, which results in the refinement of the alloy [2].…”

“…Nevertheless, they present strong disadvantages in their relatively low wear resistance and hardness, which can be a problem for long-term usage, such as in switch elements. The combination of laser surface treatment and addition of different types of metallic powders in the surface layer has been identified as a possible solution for this [1][2][3].…”